Small marine craft operating primarily in shallow water are often referred to as mud boats. Such boats are usually shallow draft flat bottom boats powered by in-board air cooled engines with outboard drives adapted to pass through the hull or transom for coupling to the engine, as disclosed by U.S. Pat. Nos. 941,827, 3,752,111 and 4,726,796.
In some cases small air cooled engines have been adapted for fixed attachment to a boat's transom for pivotal steering in the horizontal plane, with an extended drive shaft extending rearwardly to just below the water line at an angle of approximately 30 degrees as illustrated by Foreman in U.S. Pat. No. 6,302,750.
Other patents, such as Cater et al. in U.S. Des. 259,488 illustrate the use of an air cooled engine pivotally mountable to the boat's transom with the same elongated drive shaft extending to just below the waterline perhaps at a somewhat greater angle, depending on the height of the transom. In most cases the drives are designed not to extend below the bottom of the hull.
Lais et al. have also used electric motors in combination with a belt drive to maneuver small craft such as that disclosed in U.S. Pat. Nos. 5,336,119 and 1,953,599. However, obviously such drives are not intended for high speed or for extended powering through vegetation in shallow water.
The use of belt drive engines are well known within the art as being a most efficient means for driving a propeller shaft thereby reducing friction and improving mechanical advantage over right angle gear drives. Therefore, the use of a belt drive in combination with an air cooled engines as disclosed by Pignata in U.S. Pat. No. 5,435763 seems to be an obvious choice. However, Pignata utilizes a unique internal propeller arrangement and with a through the transom coupling for an inboard air-cooled engine with pivotal kick-up capability or over the top of the transom arrangement. However, Pignata fails to fully disclose how either such arrangement may be steered effectively. While the Pignata apparatus may be useful in open water it is far from obvious that it could be adapted for use in shallow water marsh with heavy mud and vegetation. The internal propeller housing must be located below the boat hull for water to be drawn effectively through the internal propeller blades. Therefore, if the propeller housing is above the bottom of the boat's hull water flow would be blocked. Shallow draft boats are known to create a depression at speed for some distance directly behind the transom it is therefore essential that the propeller shaft extend below the boat hull or beyond the water depression to make sufficient contact with the water to provide thrust and prevent cavitations.
Mud boats rely a great deal on propeller contact with the mud and the propeller's ability to cut the vegetation to help drive the boat. Hence the concept of having an elongated drive shaft extending at a shallow angle from above a boat's transom to just below the water surface has long been the excepted practice for mud boats. However, the use of a fixed inboard engine with a through transom coupling limits the apparatus to a particular boat and therefore may not be removed and mounted on another boat without extensive modifications. The use of a removable over the transom mounted air-cooled engine with extended drive shaft is awkward and often limited to a relatively low horsepower engines. There is obviously a need to provide a relatively high horsepower air cooled, efficient belt drive engine that mounts to small, flat bottom boats in much the same manner as water cooled outboard engines with a foot that does not extend below the bottom of the boat but extends a sufficient distance behind the boat to insure the proper angle of attack when the propeller is in contact with mud and vegetation.